Molded products of ethylene (co)polymer such as ethylene homopolymer, ethylene-α-olefin copolymer, and the likes are widely used for various kinds of purposes including, for example, blow molding products such as small containers, e.g. cosmetic bottles, detergent bottles, etc., middle size containers, e.g. petroleum cans, industrial chemical cans, etc., large size containers, e.g. automotive fuel tanks, drum cans, etc., molded pipe such as pipes for sewerage systems, pipes for water works, gas pipes, etc., and inflation films to be used for carry bags of supermarkets. The polymers to be employed as materials for various kinds of such molded products are required to have various properties.
For example, a blow molding product is produced by extruding a cylindrical melted resin (parison) from circular dies, pinching the resultant parison with molds, and blow molding for shaping by blowing compressed air.
Generally, in the case where a large size container is produced by blow molding, a phenomenon of sagging down of the parison owing to the self-weight (draw down) may occur or the thickness may become uneven at the time of shaping to result in defective shape of the molded products. In order to suppress the draw down, ethylene (co)polymer with a high melt tension should be selected. On the other hand, in order to suppress the thickness unevenness of the molded products or in order to give good pinch off shape of the molded products, ethylene (co)polymer with high swell ratio should be selected. Further, high impact strength or the like is required as the demanded properties of a blow molding product, and today, toughness improvement is also demanded to improve the economical properties.
A molded pipe is required to have excellent pipe fatigue characteristics, mechanical strength, and the likes. As a test for pipe fatigue properties, practically a hot inner pressure creep test, a notched tensile creep test, a notched tensile fatigue test, etc., are performed and it is desirable for the molded pipe to have excellent properties in any of the test. Recently, toughness improvement for improvement of the economical aspects, e.g. thinning of a pipe, is being demanded and excellent moldability for saving electric power consumption is also demanded.
An inflation film is required to have thickness with little unevenness, mechanical strength, and the likes. In order to suppress unevenness of the thickness, it is necessary to improve the stability of tubular melted form (a bubble) extruded at the time of molding and for that, ethylene (co)polymer with high melt tension should be selected.
The inventors of the present invention, in consideration with conventional technology, have studied ethylene (co)polymers capable of providing molded products with excellent moldability and particularly excellent mechanical strength and found that ethylene polymers and copolymers of ethylene and an α-olefin of 4 to 20 carbon atoms scarcely containing methyl branches have excellent moldability and that molded products made of these ethylene (co)polymers especially have excellent mechanical properties.
Further, the following ethylene (co)polymers are found having excellent moldability and molded products of the ethylene (co)polymers have excellent mechanical properties; ethylene (co)polymers satisfying respectively specified relations between the melt tension and the swell ratio and between the intrinsic viscosity and the melt flow rate, ethylene (co)polymers satisfying a specified relation of the number average molecular weight, the weight average molecular weight and the Z-average molecular weight, and ethylene (co)polymers having at least 2 relative maximum values and at least 1 relative minimum value in the molecular weight distribution curve respectively having the intensity satisfying a specified relation of the intensity of the relative minimum value and the lower intensity of the relative maximum values.
Finding that compositions containing such ethylene (co)polymers also have above described properties and so do graft-modified ethylene (co)polymers produced by graft modification of such ethylene (co)polymers and compositions containing such graft-modified ethylene (co)polymers, the inventors reach the present invention.
The ethylene (co)polymers produced by conventionally known methods using a Ziegler catalyst described in Japanese Patent No. 821037, a metallocene catalyst and a chromium catalyst described in Japanese Patent Laid-Open No. 9-183816, and a constrained geometric catalyst (CGC) described in WO No. 93/08221, as well as the ethylene (co)polymers produced by a conventionally known high pressure radical catalyst method contain a relatively large number of methyl branches in a molecular chain. If methyl branches exist in ethylene (co)polymer, the methyl branches are taken in crystals and make the crystals weak and the mechanical strength is, therefore, supposed to be lowered.
In the case an ethylene homopolymer or a copolymer of ethylene and an α-olefin is produced by a conventionally known method using a catalyst such as above described catalysts, the following problems sometimes happen to occur.
In the case of using a Zieglar catalyst, it becomes a problem that the produced ethylene (co)polymer contains hard and fragile components since the ethylene (co)polymer scarcely contains α-olefin and that the produced ethylene (co)polymer contains soft and weak components since α-olefin is excessively copolymerized. The components produced by excessive copolymerization of α-olefin may be a cause of sticky properties.
In the case of using a metallocene catalyst, it becomes a problem that an ethylene (co)polymer with a remarkably high molecular weight is hardly obtained.
In the case of using a chromium catalyst, it becomes a problem that the produced ethylene (co)polymer contains branched long chains to result in narrow molecular extension and inferior mechanical strength. Also, in the case of using a chromium catalyst, it becomes a problem that the produced ethylene (co)polymer contains hard and fragile components owing to scarce content of α-olefin and that the produced ethylene (co)polymer contains soft and weak components owing to excess copolymerization of α-olefin.
In the case of using a constrained geometric catalyst, the produced ethylene (co)polymer contains branched long chains to result in narrow molecular extension and, therefore, the mechanical strength is low.
The ethylene (co)polymer produced by a conventionally known high pressure radical catalyst method contains branched long chains to result in narrow molecular extension and, therefore, the mechanical strength is low.
In the case of using a catalyst containing Ta, Nb complexes, the produced ethylene (co)polymer is a low ratio Mw/Mn of the weight average molecular weight (Mw) to the number average molecular weight (Mn) measured by GPC as molecular weight distribution indexes, so that the moldability is inferior.